Recovery experts are trying to put out a coal fire and de-gas the West Coast mine where the bodies of 29 men still lie.
The workers were killed following explosions at the Pike River Coal mine near Greymouth which began on 19 November.
Pike River Coal chief executive Peter Whittall says a fire in the mine that broke out following a fourth explosion at the weekend is continuing to burn and has spread to the coal seam.
The company is hoping to use a modified jet engine, known as a GAG, to blow neutralising gases into the mine to put out the fire.
Efforts to create a seal around the mine's entrance failed on Tuesday morning when polyurethane expanding foam used to plug the gaps caught fire at 6.30am.
Police say that fire was unrelated to the coal fire and experts at the site say self-combustion of the foam is not unusual when used in large quantities.
The fire was extinguished and no one was hurt, but it has hampered progress as the portal had to be cooled down.
Police say the sealant work is almost complete, but deployment of the GAG machine will depend on the toxicity of the mine. They say gas levels remain extremely high and the build-up of gasses during the day increases the risk of another explosion.
Mr Whittall says the team will try again and the aim is to turn on the GAG machine about midnight on Tuesday.
He says it is likely a section of the coal mine's roof has collapsed. After the third explosion there was black smoke, indicating coal was burning, and that coal was likely to have come from a collapse of a section of roof or walls.
Meanwhile, Pike River Coal has begun suspending major contracts and contract workers as efforts continue to save the mine.
An Australian expert on underground explosions will fly to New Zealand to help with the recovery of the bodies.
The officer in charge of the operation, Superintendent Gary Knowles, says police have been talking daily to the expert on the phone and he has a good understanding of what is happening, but it is now crucial to have him on site.